The present invention relates generally to a system which can be used when an interventional procedure is being performed in a stenosed or occluded region of a blood vessel to enhance the expansion and deployment of an expandable cage filter for filtering the blood in a blood vessel so as to capture embolic material that may be created and released into the bloodstream during the procedure. The system of the present invention is particularly useful when performing balloon angioplasty, stenting procedures, laser angioplasty or atherectomy in critical vessels, such as the carotid, renal, and saphenous vein graft arteries, where the release of embolic debris into the bloodstream could possibly occlude the flow of oxygenated blood to the brain or other vital organs which can cause devastating consequences to the patient.
A variety of non-surgical interventional procedures have been developed over the years for opening stenosed or occluded blood vessels in a patient caused by the build up of plaque or other substances on the walls of the blood vessel. Such procedures usually involve the percutaneous introduction of the interventional device into the lumen of the artery, usually through a catheter. One widely known and medically accepted procedure is balloon angioplasty in which an inflatable balloon is introduced within the stenosed region of the blood vessel to dilate the occluded vessel. The balloon catheter is initially inserted into the patient""s arterial system and is advanced and manipulated into the area of stenosis in the artery. The balloon is inflated to compress the plaque and press the vessel wall radially outward to increase the diameter of the blood vessel.
Another procedure is laser angioplasty which utilizes a laser to ablate the stenosis by super heating and vaporizing the deposited plaque. Atherectomy is yet another method of treating a stenosed blood vessel in which a cutting blade is rotated to shave the deposited plaque from the arterial wall. A vacuum catheter may be used to capture the shaved plaque or thrombus from the blood stream during this procedure.
In another widely practiced procedure, the stenosis can be treated by placing a device known as a stent into the stenosed region to hold open and sometimes expand the segment of the blood vessel or other arterial lumen. Stents are particularly useful in the treatment or repair of blood vessels after a stenosis has been compressed by percutaneous transluminal coronary angioplasty (PTCA), percutaneous transluminal angioplasty (PTA) or removal by atherectomy or other means. Stents are usually delivered in a compressed condition to the target site, and then are deployed at the target location into an expanded condition to support the vessel and help maintain it in an open position.
Prior art stents typically fall into two general categories of construction. The first type of stent is expandable upon application of a controlled force, often through the inflation of the balloon portion of a dilatation catheter which, upon inflation of the balloon or other expansion means, expands the compressed stent to a larger diameter to be left in place within the artery at the target site. The second type of stent is a self-expanding stent formed from, for example, shape memory metals or super-elastic nickel-titanum (NiTi) alloys, which will automatically expand from a compressed state when the stent is advanced out of the distal end of the delivery catheter into the body lumen. Such stents manufactured from self-expandable materials allow for phase transformations of the material to occur, contributing to the expansion and contraction of the stent.
The above non-surgical interventional procedures, when successful, avoid the necessity of major surgical operations. However, there is one common problem associated with all of these non-surgical procedures, namely, the potential release of embolic debris into the bloodstream which can occlude distal vasculature and cause significant health problems to the patient. For example, during deployment of a stent, it is possible that the metal struts of the stent can cut into the stenosis and shear off pieces of plaque which become embolic debris that can travel downstream and lodge somewhere in the patient""s vascular system. Pieces of plaque material can sometimes dislodge from the stenosis during a balloon angioplasty procedure and become released into the bloodstream. Additionally, while complete vaporization of plaque is the intended goal during a laser angioplasty procedure, particles are not always fully vaporized and may enter the bloodstream.
When any of the above-described procedures are performed for example in the carotid arteries, the release of emboli into the circulatory system can be extremely dangerous to the patient. Debris that is carried by the bloodstream to distal vessels of the brain may cause these cerebral vessels to occlude, resulting in a stroke, and in some cases, death. Therefore, although carotid percutaneous transluminal angioplasty has been performed in the past, the number of procedures performed has been limited due to the justifiable fear of causing an embolic stroke should embolic debris enter the bloodstream and block vital downstream blood passages.
Medical devices have been developed to attempt to deal with the problem created when debris or fragments enter the circulatory system following treatment utilizing any one of the above-identified procedures. One approach which has been attempted is the cutting of any debris into minute sizes which pose little chance of becoming occluded in major vessels within the patient""s vasculature. However, it is often difficult to control the size of the fragments which are formed, and the potential risk of vessel occlusion still exists, making such procedures in the carotid arteries a high-risk proposition.
Other techniques which have been developed to address the problem of removing embolic debris include the use of catheters with a vacuum source which provides temporary suction to remove embolic debris from the bloodstream. However, as mentioned above, there have been complications with such systems since the vacuum catheter may not always remove all of the embolic material from the bloodstream, and a powerful suction could cause problems to the patient""s vasculature.
Further techniques which have had some limited success include the placement of a filter or trap downstream from the treatment site to capture embolic debris before it reaches the smaller blood vessels downstream. However, there have been problems associated with filtering systems, particularly during the expansion and deployment of the filter within the blood vessel. The filter stiffness profile is important for enabling the filter to track through the very tight and small anatomy in the blood vessels. If the filter is substantially flexible and then becomes substantially stiff, it tends to generate kinks in the guide wire, making it difficult to track through the blood vessel. Further, the filtering system may not expand substantially freely and deploy distal to the interventional procedure site, inhibiting the filtering of embolic material.
What has been needed is a reliable system and method for treating stenosis in blood vessels which improves the expansion and deployment characteristics of an expandable cage filter to enable the expandable cage to be substantially-freely expandable in the blood vessel from unexpanded condition thereof, for capturing embolic debris in the bloodstream that can cause blockage in vessels at downstream locations. The system and method should be capable of filtering embolic debris which may be released into the bloodstream during the treatment to the vessel, and yet allow a sufficient amount of oxygenated blood to flow past the filtering device to supply vital organs downstream from the treatment site. The system and method should be relatively easy for a physician to use and should provide a nearly failsafe filtering system capable of removing embolic debris released into the bloodstream. Moreover, such a system should be relatively easy to deploy and remove from the patient""s vasculature. The inventions disclosed herein satisfy these and other needs.
The present invention provides a system and method for capturing and retaining embolic debris from a blood vessel which may be created during the performance of a therapeutic interventional procedure, such as a balloon angioplasty or stenting procedure, in order to prevent the embolic debris from lodging and blocking blood vessels downstream from the interventional site. The present invention is particularly useful while performing an interventional procedure in vital arteries, such as the carotid arteries, in which critical downstream blood vessels can become blocked with embolic debris, including the main blood vessels leading to the brain or other vital organs. As a result, the present invention provides the physician with a higher degree of confidence that any and all embolic debris is being collected and removed from the blood vessel when performing high-risk interventional procedures.
The present invention is deployed in the blood vessel at a location distal to the area of treatment in the interventional procedure site, passes the blood therethrough to enable blood to flow past the filter, and filters the blood to capture and retain any embolic debris which may be created during the interventional procedure.
In the present invention, the system includes an emboli-capturing filter attached to an expandable cage to filter the blood vessel and to capture and retain embolic material, and a plurality of openings in the filter to enable some amount of blood to flow past the deployed filter. The emboli-capturing filter of the present invention directs the blood flow through the area where the interventional procedure is to be performed and through the filter located distal to the interventional site, which is designed to capture and retain friable plaque deposits. Additionally, the present invention allows blood to flow past the filter to provide a substantially continuous stream of blood to the organs located downstream.
In an embodiment of the present invention, the system includes an expandable cage and filter which can be deployed within the blood vessel for filtering blood flow past the expandable member at a location distal downstream to the interventional procedure site. The expandable cage and filter is adapted to be relatively flexible towards the distal end, and relatively stiff towards the proximal end, to provide gradual stiffness for efficient tracking through the blood vessel, and for effective expansion and deployment of the expandable cage and filter. The expandable cage and filter may include a plurality of struts, adapted to be expandable from unexpanded condition thereof. The expandable cage and filter may further include filter material which includes a plurality of openings which may be formed therein, which are adapted to pass blood therethrough while preventing embolic material from passing therethrough.
In a particular embodiment of the present invention, the system comprises a catheter, including an elongated shaft having a distal end portion adapted to be positioned in a blood vessel at an interventional procedure site. A filter device is adapted to be located in the distal end portion of the catheter shaft and is mounted on a guide wire, to be deployed distal to the interventional procedure site, and to pass blood therethrough to capture embolic material which may be released into the bloodstream during the interventional procedure. The filter device includes an expandable cage assembly, adapted to be expandable to capture embolic material, and to be collapsible to retain the captured embolic material. The expandable cage includes an element for varying the stiffness along the length of the expandable cage, for enabling the expandable cage to be substantially-freely expandable responsive thereto. The expandable cage is adapted to be positioned in the distal end portion of the guide wire, such that, for variable stiffness of the expandable cage, wherein the distal end portion is relatively flexible and the proximal end portion is relatively stiff, positioning of the expandable cage in the blood vessel is enhanced. The expandable cage further includes a plurality of struts for expansion thereof, and in another embodiment also includes a marker tip at a free end of each of the plurality of struts, adapted to be radiopaque, for enabling verification of the location of the expandable cage in the blood vessel and the opening or closing of the expandable cage.